In recent years, heat release values of electronic components have increased due to high densification and high integration of electronic components, and it has become necessary to cope with such heat. Usually, it is common to employ a method to diffuse such heat by attaching a radiator such as a heat sink, a heat-releasing metal plate or a radiation fin to a heating element such as an electronic component, and various thermally conductive sheets are used to effectively carry out thermal conduction from the heating element to the radiator.
It is widely practiced that one having a thermally conductive filler filled in a curable resin composition, is formed into a sheet, which is used as a thermally conductive sheet for heat dissipation from electronic equipments, etc. (e.g. Patent Document 1).
Patent Document 1 discloses a thermally conductive insulation sheet characterized in that a composition having a thermally conductive filler mixed to a mixture comprising a polysiloxane having C—C bonds in its molecule and an organopolysiloxane having SH groups in its molecule, is formed and crosslinked. However, a material using a polysiloxane is considered to have a problem as an environmental endocrine disrupter.
Further, one having a thermally conductive filler incorporated to a pressure sensitive adhesive such as an adhesive tape is also known (e.g. Patent Documents 2 and 3). In order to efficiently carry out thermal conduction, it is necessary to let components closely contact each other, and adhesion is commonly carried out. However, in an adhesive sheet using such an adhesive, the thickness of the adhesive layer is thin, whereby with components poor in accuracy, it has been impossible to adhere the components closely to each other.
Patent Document 4 discloses a self-supporting thermally conductive sheet excellent in flexibility and releasability, and Patent Document 5 discloses a pressure sensitive adhesive and sheet, wherein even if a thermally conductive filler or flame retardant is incorporated, the flexibility is maintained without deterioration of the adhesive strength. These sheets were flexible, but the thermal conductivity was low at a level of at most 1 W/m·K.
Patent Document 6 discloses a composition for a pressure sensitive adhesive excellent in thermal conductivity and electrical insulating properties, having incorporated a resin having specific molecular weight and acid value, and an adhesive sheet using it. The thermal conductivity and heat resistant holding power were excellent, but the amount of the filler added, was substantial, and there was a problem in conformability to special shapes such as curved surfaces.
Patent Document 1: JP-A-58-214209
Patent Document 2: JP-A-11-269438
Patent Document 3: JP-A-2000-281997
Patent Document 4: JP-A-11-292998
Patent Document 5: JP-A-2002-294192
Patent Document 6: JP-A-2004-10859